[Feature Request]: Native Android & iOS share targets (system share sheet integration)

[markoiv4]

Description

When sharing text, images, or links from other apps on Android or iOS, ChatterUI does not appear as a destination in the system share sheet. This makes it impossible to quickly send selected content (articles, screenshots, notes, etc.) into an existing or new chat without using workarounds like copy–paste or manual uploads. This limits how well ChatterUI integrates with the rest of the system and makes mobile workflows noticeably slower and more fragile.

Proposed Solution

On Android:

• Add an Android share target (e.g., via an intent-filter for ACTION_SEND/ACTION_SEND_MULTIPLE) so ChatterUI appears directly in the system share sheet.
• When invoked, let the user pick:
  • an existing chat to append the shared content to, or
  • create a new chat prefilled with the shared text/link/image.
• Optionally remember the last-used chat as a quick default target.

On iOS:

• Provide a share extension so ChatterUI shows up in the iOS share sheet for text, URLs, and images.
• The extension should send the shared content into a selected conversation or start a new one in the main app.

Nice-to-have options:

• A setting to choose default behavior (always new chat vs. last used vs. “ask every time”).
• Preserve source URL metadata (page title + URL) when sharing links.
• If possible, support multiple selected items (e.g., several images at once).